Along a section of Putah Creek in the UC Davis Arboretum, a fuzzy cloud of golden flowers seems to float above the walkway and a sweet exotic scent fills the air.
Ah, it must be (almost) spring.
Each February, scores of acacias big and small burst into bloom in the arboretum’s Conn Acacia Grove, one of the few large acacia collections in the United States. Looking like they were invented by Dr. Seuss, the individual flowers resemble little spiky puffs of yellow fluff. En masse, they blanket treetops and sprawl over slopes.
This late winter show always attracts attention as campus visitors (and honeybees) enjoy the display. The arboretum will celebrate this unusual grove with a special guided “Amazing Acacias” tour next Saturday, Feb. 24.
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But it’s what acacias can do year-round that interests Ellen Zagory, the arboretum’s director of public horticulture.
Not only are these plants pretty and fragrant when in bloom, acacias have a lot of potential to low-water landscaping, Zagory noted.
“Why is the acacia such a good plant? It’s evergreen and ornamental,” said Zagory, who has been visiting the acacia grove since she was a graduate student some 40 years ago. “It has these bright yellow flowers when few other things are blooming. And these varieties can not only take the heat but the cold.”
In addition, these fast-growing acacias tend to take care of themselves. They need little maintenance, have virtually no pests and require only monthly irrigation. In particular, that last point makes acacia worth another look right now.
“It seems like we’re headed back into drought again,” Zagory added. “One year of rain and we got all relaxed.
“Acacias have real potential (in California landscaping) because they’re super drought tolerant. In fact, when they have problems, it’s often because they got too much water.”
The arboretum’s grove lost five big trees last winter due to too much rain, she noted. The loamy soil became over-saturated and the top heavy trees blew over in a windstorm.
Native to Africa, Australia and parts of the Americas, acacia are a far-flung family often associated with hot (and dry) conditions. Some species hug the ground, forming sprawling shrubs that are good to control erosion, while other species grow into attractive 100-foot trees.
“Our collection always blooms in February,” Zagory said. “By March, (our weather) starts to warm up rapidly and the trees drop their flowers.”
Warm January weather coaxed many acacias to bloom extra early along with other late winter-flowering trees and shrubs.
“It’s been an early spring for some things,” Zagory said. “The ceanothus (California lilac) are very early; the Valley Violet (variety) is already blooming. This is the first time I can remember it blooming before the redbuds, which are coming out, too. It’s always the other way around; redbuds first, then ceanothus. That’s a sure sign something is off.”
Nearly 1,400 species of acacia are known, with about 900 native to Australia where they’re called “wattles.” The Golden wattle (Acacia pycnantha) is Australia’s national flower.
African species – a favorite food of giraffes – form menacing thorns while the Australian wattles are much friendlier (and prickle free). American acacias range from Hawaii’s famous koa trees to Southwestern desert shrubs.
For the UC Davis collection, the arboretum focused on acacias that could survive heavy frost. That’s only about 50 species.
But some have really impressed with their versatility, drought tolerance and beauty. Snowy River wattle (Acacia boormanii), an Australian native, was selected as an Arboretum All-Star and is often offered at the arboretum’s teaching nursery during spring plant sales.
“We really recommend Acacia boormanii for home gardens,” said the arboretum’s Ryan Deering, who oversees the acacia collection. “It is hardier than most and is a great narrow, evergreen plant for screening that is full of flowers in mid-February. We are using it on campus to screen parking lots and fences, in full sun or part shade under tall trees. It is very drought tolerant, too.
“I also like Acacia covenyi, blue bush acacia,” he said. “It grows quickly to about 20 feet, and has an open structure with dark brown bark and blue-gray leaves. It makes bright yellow flowers that look stunning against the blue foliage. Acacia acinacea, gold dust wattle, is another stunner, blooming so heavily in late February that it becomes a shrubby ball of bright yellow.”
Unlike most plant collections, this acacia grove started in the biochemistry department, not botany. Eric Conn, who taught at UC Davis from 1958 to 1993, focused on acacias in his research on cyanogenic compounds (such as cyanide) and how they could naturally repel insect pests. (That’s why bugs don’t bother acacias.) Founder of the university’s biochemistry department, Conn died in September at age 94.
“He loved this whole thing,” Zagory said as she walked through the grove named in Conn’s honor. “In the arboretum, (the grove) is used as a model to evaluate plant collections. We also use it to teach about foliage and plant identification. Acacias are unusual in that they have so many different forms of foliage including distinct juvenile leaves and mature leaves.”
Those leaves range from intricate fernlike foliage to straight and strong shoestrings. Some leaves are silver or blue while others stay bright green. It’s those distinctive yellow flowers that reveal these plants’ close relation.
Acacias offer more than beauty and drought tolerance, Zagory added. Many acacia tree species are valued for their wood. Flowers from other species are harvested for perfume. Gum arabic, a sap gathered from two acacia species, is used as a natural gum and stabilizer in candy such as Starburst.
“Acacias truly are amazing,” she said. “And there are so many different ones.”
Where: Putah Creek Lodge, Garrod Drive, UC Davis
When: 2 p.m. next Saturday, Feb. 24
Admission: Free; free parking
Highlights: See (and smell) scores of acacia trees and shrubs in full bloom during this guided tour.